Many industrial processes, such as various manufacturing and chemical processes take place within closed or partially closed containers or vessels, making accurate observation of those industrial processes more difficult. Accurate observation of the processes within such vessels is desirable, for example, to enable improved control and/or industrial efficiency. This is especially true where removal of product for inspection is not possible or practical, or where removal of the product would lead to inaccurate results due to the loss of process conditions.
It is known to use various devices for directly or remotely viewing the interior of a vessel, such as a pressure vessel, reaction vessel, process pipeline, or the like. A simple device for this purpose is a transparent viewing window provided in a wall of the vessel or pipeline. By looking through this window, an operator can observe liquid levels, color changes, and other visually determinable factors taking place within the vessel. Several of these viewing windows are disclosed, for example, in U.S. Pat. Nos. 2,744,487, 3,299,851, 3,837,226, and 4,245,566.
To provide for better illumination, Thomas Canty invented a light pipeline device as described in U.S. Pat. No. 4,746,178, which is incorporated by reference herein, for illuminating the interior of a pressure vessel. The device comprises a housing containing a fiber optic rod running from an external light source to a fused glass, laminated barrier disc. The unit is securely mounted on the vessel apart from a separate viewing window, with the barrier disc being arranged adjacent the interior of the vessel, whereby source light is transmitted to illuminate the vessel contents.
Combination illumination and camera viewing units are described, for example, in U.S. Pat. No. 5,230,556 to Canty et al., which is incorporated by reference herein. Units of this type include a centrally located camera for automatic viewing through a sight glass and a light guide delivering light through the sight glass adjacent the camera lens for illumination along an axis substantially parallel to the camera lens axis.
U.S. Patent Application Pub. No. 2003/0103756, which is incorporated by reference herein, describes an illumination module that provides illumination of a fluid at a point spaced inwardly from a viewing window. In addition, U.S. Pat. No. 6,450,655, which is also incorporated by reference herein, describes an illuminating and viewing unit for illuminating the interior of a vessel that includes an insertion assembly for allowing a camera lens and an illumination guide to extend into the interior of a vessel while being sealed off from the fluid in the vessel. In the system of the '655 patent, the camera is disposed exterior to the vessel, so that the deeper the insertion of the lens into the vessel interior, the longer the lens length. Longer lens lengths cannot provide the sharp focus that shorter lens length systems can provide, particularly when precise observations are desired, such as when observing tiny particles suspended in the fluid which require sharper images as those provided by short lens length cameras.